From U.S. Pat. No. 5,372,196 is previously known a percussion device, which includes a percussion piston, which is reciprocatingly movable in a machine housing. The reciprocating movement of the percussion piston is controlled by a valve device, wherein the valve element is movable to and fro in the machine housing. At its rear end, the machine housing has a space which is supplied with pressure fluid and thus drives the percussion piston in the forward direction.
A second chamber that can be pressurized is arranged for back-driving of the percussion piston. The movement of the valve device and thereby the percussion piston is controlled as a response to the position of a valve portion on the percussion piston in the housing, through periodically pressurizing a first pressure surface of the valve body. On a second, permanently pressurized pressure surface, a force is acting, which is less than the force acting on the valve body when pressurizing, because of the different areas of the pressure surfaces.
The known percussion device works well and aims at reaching percussive frequencies in the magnitude of 150 Hz. Recently set desires for higher working rate and better economy during rock drilling have however resulted in the desire for yet higher percussive frequencies and valve devices with shorter response time.